A person climbs up a stalled escalator in 60s. If standing on the same but escalator running with constant velocity, he takes 40 s. How much time is taken by the person to walk up the moving escalator?

Options

A. 37s
B. 27s
C. 24s
D. 45s

Answer

C

Explanation

Person.s speed walking only is `(1)/(60) ("..escalator..")/("second")`
Standing the escalator without walking the speed is `(1)/(40) ("..escalator..")/("second")`
Walking with the escalator going, the speed add. So, the the person.s speed is `(1)/(60) + (1)/(40) = (15)/(120) ("..escalator..")/("second")`
So, the time to go up the escalator `t= (120)/(5)=24` second.